1. Field of the Invention
This invention relates to a duct-type air conditioning system with a variable capacity fan, and especially relates to the control of fan speed and/or air pressure of said system. The invention also relates to a unique method and apparatus for inputting information to the air conditioning control system.
2. Description of the Prior Art
In traditional central air conditioning systems which distribute temperature controlled air to each room through air ducts, the required capacity of the fan differs according to each particular installation. The relationship between the total amount of air flow and static pressure in the duct in a single zone system is shown in FIG. 11. The air path resistance varies according to the length and cross-sectional area of the ducts, the shape of the duct branches, the size and shape of diffusers, etc., which vary in each installation.
In the past, a plurality of switching taps are attached to the fan motor which is installed in the heat source unit such as a gas furnace, heat pump, air conditioner, etc. The air conditioning installer determines the optimum setting of the fan speed by measuring the amount of air blown out of the diffuser and the noise level at the diffuser outlet at trial settings; then, the wiring is connected to the tap corresponding to such optimum speed setting.
There are cases wherein the optimum amount of air flow may differ between cooling and heating when the same fan unit is used for both cooling and heating. To respond to such cases, some systems automatically switch taps between cooling and heating by means of the control circuit in the air conditioning system.
The above examples relate to air conditioning systems which air condition an entire house as a single zone ("the single zone system"). On the other hand, there are systems called "multizone systems" which divide a house into a plurality of zones and control the temperature by zone. U.S. Pat. Nos. 4,406,397 and 4,530,395 are examples of multi-zone control systems.
In traditional multi-zone systems, the static pressure in the ducts is controlled at a constant level so that open dampers of one room will not have an effect on the other rooms. Unless the static pressure is so controlled, the air flow into air conditioned rooms having open dampers will increase when the number of open dampers decreases so that unpleasant conditions will occur such as the increase in the velocity of air flow and increase in noise.
Traditionally, the speed of the motor is varied according to the number of open dampers by either switching the taps of the motor by a phase controller or by controlling the power-source frequency and voltage by means of an inverter. Also, as a means to directly control the static pressure in the duct, a pressure sensor is used to control the speed of the motor so that the static pressure will be controlled at a constant level. A further simple method is to install a duct which bypasses the fan, and control the opening of a bypass damper which is installed in the bypass duct so that the static pressure will be controlled.
A control method similar to single zone systems wherein the fan capacity is automatically switched between cooling and heating is available to multi-zone systems. Further, control methods have been proposed wherein the static pressure in the duct is varied according to the thermal load in a room so that a large amount of air will be supplied to rooms having a large thermal load, and a small amount of air will be supplied to rooms having a small thermal load.
At what level the fan speed or the static duct pressure should be set is an important matter common to both single zone systems, and multi-zone systems. If the fan speed is too low, the amount of air flow is low and the efficiency of the heat source unit is not optimized. Thus, it takes a long time to reach the desired room temperature. If the fan speed is too high, the air flow from the diffuser becomes too strong creating drafts. Thus, the comfort level of the room is adversely affected as well as there being an increase in noise due to the increased rate of air flow.
A problem incurred where the fan speed is controlled only in steps by switching taps on the motor is that the optimum air flow cannot be obtained for the house. Even if the fan speed can be controlled on a continuous basis, it is a problem to easily set the optimum fan speed and resulting air flow volume.
Traditional heating systems, whether single or multi-zone, generally utilized a single heat source. Heat pump installations at times were supplemented by electric resistance heaters. If the user required more heat, he would turn on the supplemental electric heaters. Such systems did not provide for automatic selection of the heat source based upon energy costs for various energy sources or based upon ambient temperature. Thus, there was no means to optimize the heating operation if several heat sources were available in the installation.